1. Field of the Invention
This invention relates to compositions and methods for cleaning, or for removing or stripping protective coatings from, surfaces, particularly alkali sensitive metal surfaces such as those of aluminum and zinc and their alloys, while reducing or avoiding attack on the surface during the stripping and/or cleaning.
2. Statement of Related Art
Objects are often provided with protective and/or decorative coatings such as paints, varnishes, lacquers, enamels and the like. For various reasons, including defects in the coatings or desire to change to a different coating, removal of the coating may become necessary. Because of the adhesion of the coatings to the surface and the durability of the coatings, it has often been difficult to remove the coating from the surface or to which it is applied.
Removal of coatings in the prior art has usually been accomplished by contacting the coated substrate with strong chemical compositions. Such compositions have generally been alkaline materials, including alkali metal hydroxides, alkali metal carbonates, alkali metal phosphates, and alkali metal silicates. In many situations, the removal or stripping compositions have had to be used at strengths and for periods of time which resulted in appreciable attack on the substrate to which the coating was applied, particularly when the substrate was aluminum, zinc, an alloy of one or both of these metals, or some other substrate similarly susceptible to attack by alkaline liquid reagents.
Various proposals have been made to overcome these difficulties by different additives to the alkaline stripping compositions which would make it possible to decrease the time of contact or otherwise inhibit the attack on the substrate to which the coating to be removed was applied. None of these proposals heretofore have been fully satisfactory in commercial practice.